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Did vitamin D help New Zealand during the 1918-19 influenza outbreak?

Posted on: August 30, 2013   by  Vitamin D Council


Did vitamin D help New Zealand during the 1918-19 influenza outbreak? Researchers speculate that maybe it did.

The 1918-19 influenza pandemic was unusually widespread and deadly. Across the world, the influenza affected 500 million people and killed 50 to 100 million people. Even more striking was that the pandemic reached every corner of the Earth, from Pacific islands to the Arctic.

Researchers wanted to see, however, if there were any differences in incidence rates among different islands throughout the world. If there were, they wanted to know what kind of differences were there between the islands.

The researchers decided to compare the islands of Iceland and New Zealand, two relatively large islands on opposite ends of the world. The 1918-19 influenza pandemic peaked several times and both these countries were affected at the same peaks, despite being in different hemispheres.

Iceland suffered from a very high incidence rate of 66-90%, while New Zealand was much lower at 30-50%. Furthermore, Iceland had a higher mortality rate during that time, 830 per 100,000, compared to New Zealand, 550 per 100,000.

Paradoxically, when the researchers looked into the public health measures of both nations, they found Iceland had taken more and stricter actions, like firmer restrictions on public gathering.

So why did Iceland have higher incidence and mortality rate? One speculative explanation is vitamin D levels.

The researchers note that when the influenza struck both countries in November, Iceland was in sun-deprived winter and subsequent dropping vitamin D levels, while New Zealand was in summer where vitamin D levels were increasing.

While we’ll never know for sure what the protective factor was, research today shows that vitamin D can protect against respiratory infections and influenza to a certain degree. Was it the culprit in 1918? We can only guess, that yes, maybe it was.


Summer JA et al. The influenza pandemic of 1918–1919 in two remote island nations: Iceland and New Zealand. Journal of NZMA, 2013.

6 Responses to Did vitamin D help New Zealand during the 1918-19 influenza outbreak?

  1. RainyDayTreat

    What role did the war have on the infection rate in these two countries? I read the first few chapters of The Great Influenza several years ago while visiting my parents. If I recall correctly, the unusual age range of a great proportion of the victims (young-adult to middle-age males) was attributed to the mass transportation and close quarters of soldiers at this time.

  2. Rita and Misty

    Hey there, RainyDayTreat (lol),

    What interesting question. I’m definitely going to research this item. Here is an interesting link to the U.S. Military and the 1918-19 Influenza Pandemic. (if only they had supplemented with 50,000 iu D3 daily for 3 days at onset of the illness)


    “The American military experience in World War I and the influenza pandemic were closely intertwined. The war fostered influenza in the crowded conditions of military camps in the United States and in the trenches of the Western Front in Europe. The virus traveled with military personnel from camp to camp and across the Atlantic, and at the height of the American military involvement in the war, September through November 1918, influenza and pneumonia sickened 20% to 40% of U.S. Army and Navy personnel. These high morbidity rates interfered with induction and training schedules in the United States and rendered hundreds of thousands of military personnel non-effective. During the American Expeditionary Forces’ campaign at Meuse-Argonne, the epidemic diverted urgently needed resources from combat support to transporting and caring for the sick and the dead. Influenza and pneumonia killed more American soldiers and sailors during the war than did enemy weapons.”

  3. RainyDayTreat

    Hi Rita,

    Thanks for this fascinating information. It renews my interest in finishing that book I started reading at my parents’ home. I suspect that, had there been no war, there would have been no pandemic. And, of course, had they supplemented according to your prescription, there would also have been no pandemic!

  4. [email protected]

    Here’s another short summary on The Pandemic of Influenza in 1918-1919 from the Navy Dept Library.
    Soldiers had ~30+ % more incidence than civilians, probably due to being in close quarters. But the flu spread rapidly around the world, so could it be that soldiers got less sun being in heavy uniforms? I always wonder about them today, even in Iraq- completely covered up. The above article notes that vaccines are ineffective because the virus spreads too fast, and that pneumonia was the main killer.

  5. Ian

    Somehow I doubt vitamin D or sunlight exposure played a significant part in this difference.
    The (average) max uv index in October in Wellington is 7 whereas the max uv index in November in Wellington is 7.5. Of course weather varies hugely in Wellington NZ with thick cloud being the main variable. (Land of the long white cloud). so comparing November of 1918 to November of 2013 is not very reliable.

    I think troop movement might be a more valid variable with troops moving in and out of iceland more than NZ where troop movements would have been mainly out of NZ until early 1919.

  6. Ian

    I forgot, the uv index in 2013 would probably be higher than in 1918 due to the greater ozone depletion in the northern antarctic zone affecting NZ since the 50’s. So I would say that the figures I gave above are probably maxima and may have been lower in 1918-1919.

    However temperatures could also affect people. November in NZ (late spring) is warming up and more people would be getting out into the sun but I think that serum levels of vitamin D would just be starting to rise. On today’s figures, from around 20ng/ml to 23ng/ml. Would that be enough?

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